The present invention relates to a dynamic viscoelasticity measuring system which measures viscoelasticity of a material as functions of time, temperature and frequency.
The following are examples of existing viscoelasticity measuring systems: the dynamic viscoelasticity measuring system of Japanese Patent No. 2756492; the tension type viscoelasticity measuring system of Japanese Patent No. 2767634; and the viscoelasticity measuring system of Japanese Patent Laid-Open Publication No. Hei 11-218483.
The dynamic viscoelasticity measuring system disclosed in Japanese Patent No. 2756492 (called xe2x80x9cReference 1xe2x80x9d hereinafter) includes a moving mechanism for moving an electromagnetic force generator which generates AC stress to be applied to a specimen, and eliminates offset from a sine wave distortion signal. This measuring system can effectively and reliably obtain a distortion signal which is free from offset caused by thermal expansion of the specimen and a creep phenomenon and has only amplitude.
In the dynamic viscoelasticity measuring system of Japanese Patent No. 2767634 (called xe2x80x9cReference 2xe2x80x9d hereinafter), the offset of the sine wave distortion signal is eliminated using the moving mechanism of Reference 1 in order to perform the tension-type dynamic viscoelasticity measurement. Further, in order to quickly eliminate variations of static stress caused by thermal expansion or softening of the specimen, this measuring system includes the circuit designed taking the elasticity of the plate spring as the probe support into consideration. Therefore, the measuring system can prevent the moving mechansim from being very frequently moved, quickly adjust DC force, and continuously provide the specimen with tension serving as optimum static stress.
The Reference1 and 2 are aimed at effectively and reliably measuring the distortion signal. When the moving mechanism is moved in order to eliminate offset from the sine wave distortion signal to be measured by the displacement detecting circuit, static distortion and static stress of the specimen vary as described hereinafter. With respect to the static distortion, the center of the sine wave distortion signal is displaced compared with that at the initial position thereof, so that the specimen is subject to the static distortion in accordance with a moving amount of the moving mechanism. On the other hand, since the moving mechanism is moved in accordance with the deformation of the specimen, the elasticity of the plate spring applied to the specimen from the measuring system does not vary, and the static stress of the specimen also remains invariable.
In other words, it is understood that the structure for eliminating the offset from the sine wave distortion signal is designed so as to move the moving mechanism in accordance with the deformation of the specimen and to adjust the static stress of the specimen using a static stress adjustor which maintains the static stress of the specimen at a certain value.
The viscoelasticity measuring system of Japanese Patent Laid-Open Publication No. Hei 11-218483 (called xe2x80x9cReference 3xe2x80x9d hereinafter)is the static and dynamic viscoelasticity measurement system which performs two types of static viscoelasticity measurement, i.e. stress relaxation measurement by the static distortion adjuster, and creep measurement by the static stress adjustor. An operator selectively operates the static distortion adjuster or the static stress adjuster for each measurement.
However, when the References 1 and 2 in which the static stress of the specimen is adjusted using the static stress adjuster where the moving mechanism is moved in accordance with the deformation of the specimen is applied to the dynamic viscoelasticity measurement of bending type or shearing type, there are the following problems.
In the bending or shearing type dynamic viscoelasticity measurement, the specimen is preferably free from static distortion. If the moving mechanism is extensively moved and the static distortion is increased, displacement is caused between a specimen chuck and a fixedly attached specimen holder. For example, in the case of the bending type viscoelasticity measurement, the deformation center plane with respect to the bending deformation of the specimen is also distorted, so that the specimen deviates from the ideal bending deformation, which would lead to inaccurate dynamic viscoelasticity measurement.
In actual measurement, the specimen chuck tends to be slightly displaced because of warp caused by the thermal expansion of the specimen and residual stress, thereby resulting in offset in the distortion signal. In such a case, the moving mechanism is slightly moved based on the References 1 and 2 in order to maintain the bending distortion approximately equal to the ideal bending distortion and perform correction. Provided that the specimen is stiff to a certain degree and has restoring force against DC force, the References 1 and 2 can effectively allow fine correction.
However, if the specimen becomes very soft due to temperature variations or the like, it tends to creep and has only small restoring force. In this state, if the References 1 and 2 are applied, finite distortion signals, which are generated by creep due to a slight amount of DC force applied to the specimen before or during the movement of the moving mechanism and due to deviation of slight mechanical offset remaining between the distortion sensor and probe or the like, are repeatedly corrected. Especially, in the case of the bending type viscoelasticity measurement, the DC force may cause extensive deformation compared with the case where the tension type viscoelasticity measurement is performed and the DC force is the same. As a result, the offset of the distortion signal and moving amount of the moving mechanism are increased, and the specimen coupled to the moving mechanism via the specimen chuck continues its deformation. Further, since the specimen has small restoring force, it seldom returns to its initial position. In lengthy measurement, correction is repeated, so that the moving amount of the moving mechanism will be accumulated. The specimen will be subject to distortion which cannot be considered to be caused by the bending or shearing deformation.
Therefore, it is impossible to precisely perform the dynamic viscoelasticity measurement.
The Reference 3 relates to the static viscoelasticity measurement but not to the dynamic viscoelasticity measurement. Further, the operator selectively operates the static distortion adjuster or the static stress adjuster each time measurement is performed. Even if the quality of the specimen changes due to temperature variations or the like during the measurement, selective operation or cooperation of the static distortion adjuster and the static stress adjuster is not carried out in response to the quality change of the specimen. Therefore, even when the foregoing adjusters are independently operated for the dynamic viscoelastricity measurement, the following problems will occur. Specifically, when the static distortion adjuster is utilized, the warp caused by the thermal expansion of the specimen and the residual stress if forcibly suppressed, so that excessive static stress will be applied to the specimen. On the other hand, when the static stress adjuster is used, the specimen will be excessively distorted as described above.
In order to overcome the foregoing problems of the related art, the invention is intended to provide a dynamic viscoelasticity measuring system for measuring viscoelasticity of a specimen on the basis of the relationship between AC stress and AC distortion occuring in the specimen, comprising a static distortion adjuster for adjusting static distortion generated in the specimen and a static stress adjuster for adjusting static stress generated in the specimen, wherein either the static distortion adjuster or the static stress adjuster is selectively operated, or both of the static distortion adjuster and the static stress adjuster are made to cooperate, depending upon quality changes of the specimen being measured. Even when the specimen is very stiff or soft, it is possible to optimally adjust the static distortion and the static stress in accordance with quality changes of the specimen. Further, the moving amount of the moving mechanism can be maintained at an appropriate value.
The dynamic viscoelasticity measuring system of the invention operates as follows.
With the bending or shearing type dynamic viscoelasticity measurement, when the specimen is stiff and has sufficient restoring force, i.e. when an amplitude ratio of AC stress to AC distortion detected by a distortion sensor is large enough, the References 1 and 2 will be applied in order to eliminate influences such as warping caused by the thermal expansion of the specimen and the residual stress. For instance, when the amplitude ratio is larger than a predetermined maximum value, the static stress adjuster will be used to adjust the DC force applied to the specimen to zero. Further, the moving mechanism will be effectively moved in order to precisely perform the dynamic viscoelasticity measurement.
If the specimen becomes too soft due to temperature variation and so on, i.e. when the amplitude radio of the AC force to the AC distortion detected by the distortion sensor is sufficiently small, influences such as deformation stress caused by the thermal expansion of the specimen and residual stress are negligible. For instance, when the amplitude ratio is below a predetermined minimum value, the static distortion adjuster will be operated in order to stop the moving mechanism, reduce a varying speed of the static distortion to zero, and apply slight DC force to the specimen, thereby reducing the offset of the distortion signal to zero.
In accordance with the invention, the dynamic viscoelasticity measuring system measures the viscoelasticity by selectively operating the static distortion adjuster or the static stress adjuster. If the dynamic viscoelasticity measurement is performed by cooperation of these adjusters, it is possible to eliminate influences such as the warp caused by the thermal expansion of the specimen and the residual stress, and to maintain the moving mechanism at its intial position if the specimen has little restoring force. Further, the specimen is protected against excessive distortion, and can maintain ideal bending or shearing distortion.